Much of the Northeast is choking beneath a thick blanket of smoke as Canadian wildfires in Ontario and Quebec continued to burn late into the week. Some of the worst smoke has descended upon major cities in the State of New York, including Syracuse and New York City. The latter had some of the worst outdoor air quality in the world for any major city on Tuesday, while the air quality index (AQI) in Syracuse exceeded 400 on Wednesday afternoon.

“It’s looks like a sci-fi movie,” according to Patricia Paz, a retiree and resident of Manhattan’s Upper East Side. “It is really weird.”

As of Wednesday afternoon, the severity of the smoke had turned the skies over the five boroughs an eerie shad of yellow and the oppressive smell of woodsmoke filed the air as the AQI approached 325. The smoke was so severe by midday that the Federal Aviation Administration issued a temporary ground stop for New York’s LaGuardia International Airport.

While the East Coast of the U.S. has largely been spared extreme wildfire events over the years, the extent of the smoke from the Canadian fires is a reminder that people from hundreds or even thousands of miles away can be impacted. Consequently, smoke resiliency is not just an issue for those who are in near areas that are prone to fires; it can even affect those living half a continent away.

The Path to Resiliency

Passive House construction affords occupants resilience from several types of emergencies. The continuous insulation, airtight construction, lack of thermal breaks, and high-performance windows that are central to Passive House principles keep buildings at a persistent temperature, even when active heating and cooling systems are unavailable. When grids remain intact, as is the often the case during extreme smoke events, the mechanical ventilation required in passive construction ensures a steady supply of fresh, filtered air.

Resiliency was only one of the reasons why homeowner Chad Dickerson decided to perform a deep energy retrofit on his rowhome located along the picturesque streets of Brooklyn’s Cobble Hill neighborhood. Dickerson and the architecture team from Baxt Ingui Architects ultimately had the home certified through the Passive House Institute’s EnerPHit program.

While resiliency was a concern, it had also been one of the least noticeable benefits of Passive House construction. In fact, Dickerson had only recently become more aware of the improved indoor air quality within his home after purchasing several indoor air quality monitors.

The monitors had been regularly reporting levels of fine particulate matter (particulates 2.5 microns in diameter or smaller [PM2.5]) ranging between 1-3 µg/m3, with temporary spikes in the kitchen while cooking (see Table 1). With conditions deteriorating outside Tuesday evening, Dickerson expected to a see somewhat elevated levels on his monitors. To his chagrin, the PM2.5 levels surpassed the high end of the range by a wide margin. In several rooms they were hovering around 70 µg/m3 or even higher, which meant his air had gone from good to unhealthy.

Clearly something was wrong.

Putting the Filter in Filtration

Dickerson began troubleshooting and found several recommendations online. This only added to the confusion.

“A number of people who went through the California wildfires noted how an ERV doesn't necessarily filter out all the smoke particles,” Dickerson wrote in an email exchange. Meanwhile, some vendors recommended turning the ERV completely off during high smoke periods, while others recommend putting the unit into "exhaust only" mode.

He tried the latter, but the levels in the house weren't getting better after an hour. Eventually, he decided to check the filters.

“I change the filters every two months and realized they were due to change on June 13,” he wrote. “The supply filter was filthy! I changed the filters a little early and the air quality in the house started getting better almost immediately even as the air worsened outside.

“I was already happy with the Passive House setup but seeing it in these conditions made me even happier. I just needed to change my filters to make it work optimally. The lesson is CHECK YOUR FILTERS (and change them if necessary) in these conditions!”

Despite the rapid improvements Dickerson saw, conditions continued to get worse in the city, eventually reaching a score of 325 on Wednesday before relenting some. In a case this severe, even the improved filtration on the ERV could not keep the PM2.5 levels as low as Dickerson would have liked and it appears that even an AQI of 200 may be too much for the system to handle. The lesson here, unfortunately, is that supplemental filtration is sometimes necessary even in a passive home.

Ultimately, he put the ERV into “away” mode and set an alarm to check the outdoor AQI. So long as it stayed above 200, the system remained off. As a temporary solution, he plugged in a Honeywell HPA 304 air purifier that he had sitting around and put that to use in his family room. “For some reason, I always doubted if those things actually worked but the indoor PM2.5 levels improved extremely quickly with it on, so now I'm a believer,” he wrote. “We plan to get at least one more to have on hand for any future events. It worked so well that it made me think that an add-on filtration system on the ERV might not be necessary given the (hopefully) somewhat rare incidence of these sorts of wildfires. I think you could just close off some rooms and use one of these in the rooms you're in to ride out the smoke.”

Since the AQI outside dropped below 200, the ERV has been running normally and the PM2.5 levels inside stabilized. They were in the low 30s µg/m3 by early Thursday morning and have since fallen to a range of 17-25 µg/m3 as of Thursday afternoon.

Filtering for Wildfires

According to John Semmelhack of The Comfort Squad, filtering out volatile organic compounds (VOCs), fine particulate matter that is 2.5 microns and smaller (PM2.5), and other toxins requires a combination of filtering techniques, even in homes that are extremely airtight and even Passive House certified. At times of increased air pollution, such as during or immediately following a wildfire event, MERV-16 or HEPA filtration outside the air intakes of ERVs is necessary to control PM2.5 levels. “Homes with MERV-15 and lower filtration on ERV intakes showed significantly elevated PM2.5 levels during wildfire events,” Semmelhack says. “It’s also always a good idea to have stand-alone portable filtration available (either DIY or purchased) for an extra boost to capture anything that makes it past the ERV filter.”

MERV-16 or HEPA filtration on the ERV intake can also help filter out VOCs, other toxins, and odors. However, Semmelhack adds that these pollutants may not always be attached to fine particles and that carbon filtration (also known as “charcoal filtration” or “activated charcoal”) is the only type of filtration that is effective for eliminating VOCs and odors.

Top photo of the New York City skyline by SnowFire.